1. Field of the Invention
The invention pertains to the field of point of care tests. More particularly, the invention pertains to lateral flow assays.
2. Description of Related Art
Lateral flow assays are a subset of assays combining various reagents and process steps in one assay strip, thus providing a sensitive and rapid means for the detection of target molecules. Antibody-based lateral flow immunoassays are available for a wide range of target analytes and can be designed for sandwich or competitive test principles. Generally, high molecular weight analytes with several epitopes are analyzed in a sandwich format whereas small molecules representing only one epitope are detected by means of a competitive assay. The first tests were made for human chorionic gonadotropin (hCG). Today there are commercially available tests for monitoring ovulation, detecting infectious disease organisms, analyzing drugs of abuse, and measuring other analytes important to human physiology. Products have also been introduced for veterinary testing, environmental testing, and product monitoring.
In the prior art, the mobile labeled receptor (also known as the tracer or the test conjugate herein) in these assays is either dried on the test strip, contained in an external eluting solution (such that it can be pre-mixed with the sample prior to application on the test strip), or part of the elution media.
European patent publication EP0582231, published Feb. 9, 1994, entitled “SOLID PHASE ASSAY”, discloses an assay with a porous solid support with a first portion that contacts a sample that may include an analyte of interest. The sample flows through the solid support, and the analyte, if present, combines with a tracer, which is reversibly bound on the solid support. The sample and the tracer initially travel in a direction perpendicular to the first portion (e.g. vertically) via capillary flow. The tracer and analyte then continue to travel by capillary flow through the material to a second portion that includes an immobilized binder, which binds to the analyte in a sandwich immunoassay format. Travel to the second portion occurs in a direction perpendicular to the direction in which the tracer and sample initially travel (e.g. laterally). All travel of the sample and tracer occur due to capillary flow through the device. Although travel occurs vertically and laterally, there is a single flow path. The sample, the tracer, and the immobilized binder are all in the same flow path.
U.S. Patent Publication No. 2007/0224701, published Sep. 27, 2007, entitled “COMBINATION VERTICAL AND LATERAL FLOW IMMUNOASSAY DEVICE”, discloses immunoassay devices, kits, and methods for determining the presence or absence of an analyte in a liquid sample using a combination of vertical flow and lateral flow. The device includes a tracer pad with a labeled receptor that is vertically juxtaposed with a binder support medium. The device disclosed in this publication is multi-sectioned, but, similar to EP0582231, only has a single flow path. The sample, the labeled receptor, and the binder support medium are all in the same flow path.